1. Field of the Invention
The present invention relates to toner supplying devices appropriately utilized for image forming apparatuses such as printers, facsimiles, copiers, hybrid apparatuses, in particular electrophotographic image forming apparatuses; and toner supplying processes, image forming apparatuses, and image forming process that utilize the toner supplying apparatuses respectively.
2. Description of the Related Art
Toner supplying devices are widely utilized in image forming apparatuses such as printers, facsimiles, and copiers in order to convey toner through conveying pipes usually equipped with a movable member such as a screw auger. In such toner supplying devices, there exist some problems that toner agglomerates generate due to toner softening derived from intense rubbing of toner between the movable member and the pipe wall, and dynamic properties of toner changes due to separation of external additives from toner surface, resulting in adverse effects on images. Recently, toner with lower softening temperatures is desired in order to reduce fixing temperatures as low as possible, which accelerating generation of toner agglomerates i.e. so-called secondary particles.
In order to solve such problems, Japanese Patent Application Laid-Open (JP-A) Nos. 2003-330218 and 2004-4394 propose a toner supplying device. In the toner supplying device, pressure generated by rotating a stator with uniaxial eccentric screw and double-start spiral holes is utilized to convey the mixture of toner and air without a coil screw, and the toner is supplied to the developing unit or the related storage tank from a separately disposed toner storage unit, toner supplying unit, or the like. Further, screw pumps or so-called mono pumps are known that are utilized to convey the mixture of toner and air by means of pressure generated in situ.
In such conveying devices, there exist some advantages that the conveying distance may be easily extended, the conveying devices are compacted, the configuration is simplified, and the maintenance is relatively easy. Specifically, as shown in FIG. 1, the conveying device is equipped with screw pump 211 such as a mono pump that conveys a mixture of air and toner, toner container 212, nozzle 213 that is disposed at bottom of the toner container 212 and act to suck the toner, air pump 218, aperture 214 that connects to the air pump 218, conveying pipe 215, and filter 219. Air is intermittently directed from air pump 218 through aperture 214 into toner container 212, thereby a mixture of air and toner is formed, and the fluidized toner is directed to the toner outlet and conveying pipe 215. The mixture of toner and air directed into the conveying pipe 215 is further directed to developing unit 216 by the sucking action of mono pump.
Such toner conveying devices provide advantages that the toner may be easily conveyed to the developing unit or the related storage container due to the higher fluidity of the mixture of air and toner, and the residue of toner may be reduced in the toner container.
However, such toner conveying devices suffer from a problem that the air fed into the toner container cannot satisfactorily break secondary toner particles in the toner container. Namely, the air fed near the nozzle forms larger bubbles in the mass of toner within the toner container; the bubbles move and/or burst in the mass of toner and thus the mixture of air and toner is formed, which exhibits relatively high fluidity; however, the secondary toner particles that have been present prior to the air feeing hardly break by the air feeding into the toner container, consequently, the secondary toner particles tend to deteriorate image quality. This problem is serious with respect to nowadays highly fine and precise images since toners are required that have smaller particle sizes.
Further, another toner supplying device is proposed wherein a larger toner container is provided outside an image forming apparatus, and toner is supplied from a larger toner container to a developing unit of the image forming apparatus. However, the device also employs a screw pump similar to that of JP-A Nos. 2003-330218 and 2004-4394 described above; thus the toner supplying device suffers from similar problems described above.
Further, there exist image forming apparatuses of direct recording as shown in JP-A No. 2000-238311, in addition to those of electrophotography. In such image forming apparatuses, toner is applied as droplets onto recording media such as recording paper, thereby images are recorded directly. In such image forming apparatuses also, the friction of toner due to movable parts is undesirable and desired to eliminate, for example, by conveying the toner to an ink applying device by means of sucking unit such as a suction pump.
However, such a toner conveying device suffers from a problem that the air fed into the toner container cannot satisfactorily break secondary toner particles in the toner container as described above. Further, in the toner conveying device, the conveying line often clogs and the operation is disturbed when the image forming apparatus is stopped for a few days for example, which is resulted from solidification or blocking of toner within the conveying line.
Further, the mixture of toner and air formed by the toner conveying devices in the prior art may not exhibit sufficient fluidity when the conveying distance is longer or when the mixture is to be conveyed from lower site to higher site, which limits the design and/or layout of image forming apparatuses.
In addition, as for the reason of clogging within conveying lines, the toner flowing into the conveying pipe has various bulk densities depending on stirring conditions and residence times; the toner with higher bulk densities tends to clog within the conveying pipe.
In order to address such a problem, the image forming apparatus illustrated in JP-A Nos. 2003-330218 and 2004-4394 described above is equipped with a nozzle in a toner containing portion and a gas feeding unit such as a blower to feed gas into the nozzle periodically. The periodical stirring of the toner in the toner containing portion by gas may avoid excessive increase of the bulk density.
However, the lower bulk density is often no more than temporary; that is, the bulk density tends to increase rapidly under sucking action. Although not wishing to limit the present invention to any one theory, the reason is believed that when the toner is sucked out from the toner containing portion, the gas existing relatively apart from the toner is sucked in addition to the toner and the surrounding gas, and gas is sucked preferentially than the toner. When allowing to stand the toner a few days in a condition of higher bulk density within conveying pipes for example, larger blocks of toner are likely to yield, resulting in clogging of the conveying pipes.
Further, frequent air blows from nozzles has been tried in order to prevent the clogging within the conveying lines. However, frequent air blows cannot successfully prevent the clogging in most cases. Although not wishing to limit the present invention to any one theory, the reason is believed that the gas blown from nozzles does not necessarily spread into the toner containing portion uniformly, nonuniform zones inevitably exist. Consequently, toner with higher bulk densities flows into conveying lines, and when allowing to stand the toner a few days, larger blocks of the toner are likely to yield, resulting in clogging of the conveying pipe.
As such, toner supplying devices and the related technologies are demanded still that may control the bulk density of the mixture of toner and gas more efficiently thereby the fluidity of the mixture is enhanced, the fluidity may be maintained uniformly within toner conveying lines even when toner resides for a long period, higher image quality may be obtained even under prolonged usage of image forming apparatuses, and toner may be conveyed smoothly at the staring operation even after longer stoppage.